Driven by unprecedented bloodshed in Trenton and the most violent 12-month stretch in Newark in nearly a quarter-century, homicides across New Jersey jumped to a seven-year high in 2013, a spike prosecutors and police officials tied to understaffed departments and a growing disregard for life.

A Star-Ledger survey of county prosecutors’ offices found at least 409 people died violently last year.

More than a quarter of those killings took place in Newark, where a spate of Christmas season slayings pushed the homicide total to 111, including one in the final hours of the year. The tally is the highest since 1990. In Trenton, the number of homicides soared to 37, the most in the state capital’s recorded history.

Both cities have been fighting crime with hundreds fewer police officers than they once had, the result of layoffs in 2010 and 2011. Law enforcement officials say they’re also confronting an increasing callousness, particularly among young people.

In Newark, where police Tuesday charged a 15-old-old boy with a Christmas Day shooting that left two teenagers dead and a third seriously injured, Police Director Samuel DeMaio called the case indicative of the culture of violence.

The alleged shooter, law enforcement sources told The Star-Ledger, opened fire because he felt "disrespected" by one of the victims in a dispute over a girl. A stray bullet struck 13-year-old Zainee Hailey, killing her, as she took out the trash.

"This new young generation is the most violent — and has the most disregard for life — that I’ve seen in my 28 years of law enforcement here in Newark," DeMaio said. "Every generation just seems to keep getting worse and worse and worse. These kids have no expectation to live past 25, and why should they?"

The Newark killings, along with a triple murder outside an Irvington go-go bar and the high-profile shooting death of a Hoboken attorney outside the Mall at Short Hills, contributed to a 20 percent increase in homicides in Essex County, the biggest jump of any county in the state.

Other cities that often rank among New Jersey’s most violent enjoyed progress in 2013.

Led by a 50 percent decrease in homicides in Elizabeth, Union County saw slayings drop for the second year in a row, and Atlantic City enjoyed its lowest homicide total in nearly 30 years.

In Camden, where the state’s first regional police force took over from city police this year, homicides fell to 57 from a record-high 67 in 2012.

OLD PROBLEMS

The refrain from law enforcement is familiar.

An influx of high-powered guns and former drug convicts looking to reclaim their turf, combined with a decrease in the number of police officers patrolling New Jersey’s streets, loomed large in the statewide spike.

Mercer County Prosecutor Joseph Bocchini said Trenton’s overwhelmed police force struggled to contain ongoing disputes between local drug crews as the city broke its prior record of 31 killings. That mark, set in 2005, came in the wake of brutal gang wars between the Nietas and Latin Kings street gangs and in the same year the Bloods took control of the drug trade in the state capital.

Now, Bocchini said, some of the names have changed, but the issues remain similar.

"Some of it’s gang, but it’s not gang the way it was back in 2005 when we initiated the county gang task force," he said. "A lot of it, they may be gang members, but they’re more like neighborhood disputes."

Bocchini said police department staffing has played a major role.

"Obviously, when you lose one third of your force, you’re going to have substantial problems," he said. "They are just so overloaded. You’re out, a crime is committed, you have a report to write, another crime is committed and you’ve gotta leave and go back out in the field."

The toll in Trenton might have been higher had a contingent of state troopers not been deployed there in mid-August, dramatically slowing the frequency of killings.

A CALL FOR GUN CONTROL

In Newark, DeMaio reported similar struggles. All too often, he said, drug convicts who returned to the streets wound up outgunned by younger, well-armed dealers who had crept onto their corners.

DeMaio said .45-caliber handguns — far more powerful than the 9 mm weapons once common in Newark — and the proliferation of assault weapons led to the city’s increased number of killings.

"If the federal government is really serious about gun control and the violence that’s taking place, not just in Newark, but in every city throughout this country, they will get strict and do the right thing with the gun laws," he said. "Make them consistent. … Take the guns out of the criminals’ hands."

While homicides and robberies surged, other crimes fell in Newark, DeMaio said. A new task force created to combat nonfatal shootings in the wake of a 2012 Star-Ledger report helped Newark decrease that crime by 23 percent, he said.

Other cities that suffered major layoffs in 2010 and 2011 made their first gains against violent crime in years.

With only three homicides in 2013, Atlantic City saw its lowest number of killings in nearly 30 years, records show.

Paul Loriquet, a spokesman for the state Attorney General’s Office, said improved casino security, along with state- and federal-backed takedowns of two of Atlantic City’s largest gangs, played a key role in the dip.

In Camden, Police Chief Scott Thomson said he hopes to build on the success of the new regional police force as the department gains nearly 150 new officers in 2014.

"Considering the Metro (Camden Metro Police) launched on May 1 and did not surpass previous staffing levels until just last week, the progress made thus far has been outstanding by all accounts," Thomson said. "The community loves the engagement from the walking beat cops, and the officers have diligently responded with a 70 percent increase in seizures of illegal firearms."

Jersey City homicides increased last year for the first time since 2009, climbing from 13 to 20. First-year Mayor Steven Fulop blamed the surge on a gang war that left seven people dead in July. The dispute coincided with a mass retirement in the police department’s top ranks.

"We had 25 senior officers retire to take pension payouts," Fulop said. "A gang war ensued, so there was back and forth, and we had a really tough July. But we got our arms around it."

The increasing use of guns to settle petty disputes has played a significant role in the violence, police leaders say. Aware that many killings in Newark are targeted, and often perpetrated by several well-armed gunmen, DeMaio wondered how he is supposed to stem homicides in the city’s shadowy drug sub-culture.

"Those are the types of jobs where somebody makes a decision that they are going to kill Person A," DeMaio said, "and barring somebody calling us ... how do you stop that murder?"